There's no dedicated connector for 12S, only 12N (behind the O/S/R upper tail light cluster, as already said).
The Land Rover 12S Kit picks-up two connections from the 9-way Trailer Pickup Connector in the vehicle's loom, these are -
Green/Brown trace (GN) wire - Reverse Lights - to Pin 1 on 12S (Yellow wire)
Purple/Brown trace (PN) wire - Permanent Fused Live (from F9 (25A) in the under-bonnet fusebox) - to Pin 4 on 12S (Green wire)
(The Yellow and Green wires have the correct Sumitomo Male Terminals and Wire Seals on them, to replace blanks in the Male Connector that is part of the 12N Kit)
The Earth from Pin 3 on 12S (White wire) has an eyelet terminal which goes to an Earth Stud behind the O/S/R trim.
The Blue and Red wires for Caravan Battery Charging and Caravan Fridge are taken from an ignition switched live at the under-bonnet fuse box, via a Voltage Sensitive Switch, a couple of Fused Relays and a long loom run along the chassis in convoluted tubing.
For the Discovery II, Land Rover sell three diferent 12S kits, they are -
STC50179 - For pre-1999 caravans (split-charging controlled on the towing vehicle)
STC50389 - For caravans 1999 onwards (power distribution incorporated in the caravan electrics)
STC50180 - No fridge or charging circuit included
If you wanted to make your own from a universal 12S Kit, then you might find reference to the Land Rover Instructions useful -
This is for
STC50179 -
http://topix.landrover.jlrext.com/topix/service/document/62736
.